American teenagers experience a conflicting mix of "altruism and cruelty" on social-networking sites like Facebook, according to a report released today.

On one hand, 88 percent of teens have seen "mean and cruel" behavior on social-networking sites and 15 percent have been the direct target, according to a new Pew Research Center study.

Yet 80 percent of those teens say they have come to the defense of a targeted social-networking friend. And 78 percent say that a social-networking experience made them feel good about themselves or deepened a friendship with another person.

Pew's latest Internet & American Life Project report isn't intended as a recipe for how teenagers or their parents can avoid bullying or cruel behavior, either online, on the phone or in person, said Pew senior research specialist Amanda Lenhart, who co-authored the study.

"The key is realizing that most teens feel that social media is a pretty good place and one where they are deepening friendships and feeling good about themselves," Lenhart said. "For a subset of kids, social media isn't all sunshine and rainbows, and parents' role is to do their best to figure out when teens are really getting bogged down in the negative experiences on social media rather than simply muddling through teen experience."

But she added, "Easier said than done, of course."

The use of social networks, especially Facebook, has become nearly universal for American teenagers. About 95 percent of all teens ages 12 to 17 are online and 80 percent of them use social networks. That compares with 55 percent of the teens on social networks when Pew started measuring that behavior in 2006.

The latest study, conducted from April 19 to July 14, surveyed 799 teens and their parents. The study asked online teens about their experiences with "mean and cruel behavior," such as name calling and teasing, but questions about bullying encompassed both online and offline behavior. And Lenhart said that even among teens, there are wide interpretations about what those terms mean.

Among teens, a social-networking experience caused 25 percent to have a face-to-face argument, 22 percent to end a friendship, 13 percent to feel nervous about going to school the next day and 8 percent to get into a physical fight.

"Often teens felt bolder, ruder, or more empowered because they did not fear physical violence in the online space," the report said. "One middle school girl told us that she thought people were ruder online 'because you can't hurt anybody online. You can't punch nobody through the screen.'"

On the other hand, the report quotes a high school boy who says people are more open on Facebook than in person. "Some things that might be awkward in real life won't be that awkward in a conversation on Facebook," he said.

Bullying wasn't limited to social networking, however. About 12 percent reported being bullied in person, 9 percent by text message, 8 percent by e-mail, social networking or instant messaging and 7 percent by voice calls over the phone.

The study did find parents are increasingly active in monitoring their teens' online behavior. Eighty percent of parents who use social media also have friended their children, although 18 percent of those teens still experienced a negative social-networking experience.

And that highlights an age-old dilemma for parents, who "can't always be everywhere, online or off," Lenhart said. The study is "a good reminder that actions like friending your teen on a social network site isn't a panacea."